1. Field of the Invention
The present invention relates to a method of forming a capacitor for a semiconductor memory device. More particularly, the present invention relates to a method of forming a capacitor having a TaON film as a dielectric film, in a semiconductor memory device.
2. Description of the Prior Art
Along with the recent progress in the semiconductor manufacturing technology, the demand for memory device has increased dramatically. Generally, a memory device having high capacitance is desirable. Capacitance of the capacitor can be increased by using a dielectric layer having high dielectric constant or enlarging the surface area of a lower electrode. Those conventional capacitors are made with a Ta2O5 layer having a dielectric constant higher than that of nitride-oxide(NO), thereby forming the lower electrode of 3-Dimensional structure.
However, as the Ta2O5 film has an unstable stoichiometry, it must be subjected to an oxidation process for making it a stable state after being deposited. Upon this oxidation, the Ta2O5 film is easily reacted with the lower electrode. This results in an increase in thickness of the effective dielectric film, thereby causing a decrease in capacitance of the capacitor. In addition, as the Ta2O5 film is formed from an organic tantalum metal material as a precursor, there remain a large amount of carbon compounds in the Ta2O5 film so that leakage current tends to generate.
To solve such drawbacks with the Ta2O5 film, we have previously proposed a capacitor using a TaON film as a dielectric substance, as described in Korean Patent Application No. 99-24218. Such a capacitor using the TaON film as the dielectric substance is shown in FIG. 1.
Referring to FIG. 1, a gate electrode 13 including a gate insulating layer 12 at a lower portion thereof is formed according to a known technique on the upper part of a semiconductor substrate 10 which a field oxide layer 11 is formed at a selected portion thereof. A junction region 14 is formed on the semiconductor substrate 10 at both sides of the gate electrode 13, thereby forming an MOS transistor. A first interlevel insulating layer 16 and a second interlevel insulating layer 18 are formed on the upper part of the semiconductor substrate 10 in which the MOS transistor is formed. A storage node contact hole h is formed inside the first and the second interlevel insulating layers 16,18 so that a junction region 14 is exposed. A cylinder type lower electrode 20 is formed according to a known method, inside the storage node contact hole h so as to be in contact with the exposed junction region 14. A HSG(hemi-spherical grain) layer 21 is formed on a surface of a lower electrode 20 to increase the surface area of the lower electrode 20 more. The surface of the lower electrode including the HSG layer 21 is thermal annealed at a temperature of 850xc2x0 C. to 950xc2x0 C. under a NH3 plasma gas atmosphere for the purpose of preventing a natural oxide from being generated. A silicon nitride film 22 is formed by thermal annealing, on the lower electrode 20 including the HSG film 21 and on the second interlayer insulating film 18. Natural oxidation reaction of the lower electrode 20 is restrained by forming the silicon nitride film 22. On the silicon nitride film 22, there is formed a TaON film 23 by a chemical vapor deposition of tantalum chemical vapor, NH3 gas and O2 gas. Then, the TaON film is crystallized by a thermal annealing, after which an upper electrode 25 is formed on the crystallized TaON film 23. This TaON film 23 has a very high dielectric constant (∈=20 to 25), and consists of stable Taxe2x80x94Oxe2x80x94N bonds. For this reason, the TaON film 23 does not need to be subjected to an additional oxidization processing for the conversion into a stable state after being deposited, and also does not result in an increase in its thickness by virtue of its very low oxidation reactivity.
However, as the thermal annealing for the prevention of the natural oxidation film generation, which is carried out before the deposition of the TaON film 23, is proceeded at 800xc2x0 C. or above, the lower electrode 20 and other electrodes are melted that are made of material having a melting point of 800xc2x0 C. or below. Thus, it is actually impossible to conduct the thermal processing at 800xc2x0 C. or above.
Meanwhile, another method was previously proposed in which the thermal annealing before the deposition of the dielectric film is carried out at a temperature of 700xc2x0 C. or below. However, if the thermal annealing is carried out at 700xc2x0 C. or below, capacitance of the resulting capacitor can be increased as compared with the case of performing the thermal annealing at 800xc2x0 C. or above as shown in FIG. 2A, whereas a leakage current characteristic can be deteriorated as shown in FIG. 2B.
Accordingly, it is the object of the present invention to provide a method of manufacturing a capacitor for semiconductor memory devices capable of occurring less leakage current and obtaining high capacitance.
According to an embodiment of the present invention, there is provided a method of forming a capacitor on a semiconductor substrate, comprising the steps of: forming a lower electrode on the semiconductor substrate; forming an O3-oxide film on the lower electrode; forming Sixe2x80x94Oxe2x80x94N bonds on the surface of the O3-oxide film; forming a TaON film on the Sixe2x80x94Oxe2x80x94N bonds by a chemical vapor deposition of a Ta chemical vapor, an O2 gas and a NH3 gas; and forming an upper electrode on the TaON film.
According to another embodiment of the present invention, there is provided a method of forming a capacitor on a semiconductor substrate, comprising the steps of: forming a lower electrode on the semiconductor substrate; forming an O3-oxide film on the lower electrode by being supplied with an O3 gas at a temperature of 200xc2x0 C. to 500xc2x0 C.; forming Sixe2x80x94Oxe2x80x94N bonds on the surface of the O3-oxide film; forming a TaON film on the Sixe2x80x94Oxe2x80x94N bonds by a chemical vapor deposition of a Ta chemical vapor, an O2 gas and an NH3 gas at a temperature of 300xc2x0 C. to 600xc2x0 C.; thermally processing the TaON film; and forming an upper electrode on the TaON film.